Thanks from the both of you ill be getting help from my Dad, he's had Lambrettas from the age of 16 so he has plenty of experience , yeah it's definitely a 50, the engine number is J50 * 58(and so on). Just out of interest what makes you think different?

Woah, that's certainly thin looking at the barrel spigot/skirt, is there a bit missing to the right of the top inlet?. What does it measure across the bore? Perhaps someone in Italy thought it should have been 75cc and not 50cc

Yeah one of the spigot lugs have snapped at some point in time, I haven't been out in the garage today so I haven't took any measurements. All I know is that the piston is an Asso with the number 44 on it. Presumably a 44mm piston?

I've just clicked on, you're on about the Black one? That's out of a Montessa, kindly given to me by Snails (Ed). I've since taken that out and replaced it with an original Veglia one courtesy of Jem Booth.